Signaling system



Aug. 25, 1942.

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l OPERATORS POSITION & KEV SET CIRCUIT H. E. VAUGHAN SIGNALING SYSTEM Filed Sept. 14, 1940 2 Sheets-Sheet l J2 is OUTGO/NC I 7' INCOMING mun/r TRUNK CIRCUIT CIRCUIT SIGNAL RECEIVING CIRLUIT SENDE'R CIRCUIT lA/l/E/V TOR H. E. VAUGHAN Aug. 25, 1942. H. E... VAUGHAN SIGNALING SYSTEM Filed Sept. 14, 1940 2 Shets-Sheet 2 Q? a y vAvA All

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M AM -5 L'Qi AA MA 1/2 lNl/ENTOR H. E VAUGHAN A TTORNEV Patented Aug. 25, 1942 SIGNALING SYSTEM Henry E. Vaughan, Valley Stream, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application September 14, 1940, Serial No. 356,716

Claims.

This invention relates to signaling systems and particularly to voice frequency signaling in automatic and semiautomatic telephone systems.

It is the object of the invention to increase the adaptability, reliability and efficiency of voice frequency signaling and to provide a Voice frequency signal receiver which is arranged to receive and selectively respond to an increased number of separate signals.

This invention is a voice frequency signal receiver arranged to receive and respond to a first or conditioning signal comprising current of a first particular frequency followed by current of a second particular frequency, and thereafter to any one of twelve other signals, each other signal comprising current of a different one of twelve signaling frequencies including said first and second particular frequencies. According to one feature of the invention, the signal receiver is arranged so that each of twelve signal relays is selectively connected for response to signaling current of a different one of the twelve frequencies. The arrangement is one in which proper signal response is unaffected by variations in the energy level of the signaling current and differences in the level of the various frequencies at the signal receiver, providing the signal current of each frequency is high enough to effect the operation of a signal relay.

According to another feature of the invention, a signal receiver comprises a plurality of signal relays, each arranged for selective response to current of a different one of a corresponding plurality of frequencies, only one of the signal relays being normally operable, the operation of this relay being effective to render a second one of the relays operable, and the operation of this second relay within a predetermined, interval of time after the operation of the one relay being effective to render the other signal relays operable.

A clear and complete understanding of the invention will be facilitated by considering a system in which the invention is embodied, one such system being shown schematically in the drawings which form a part of this specification. The invention is not limited, however, in its applicat-ion to the particular system shown in the drawings but is generally applicable to any voice frequency signaling system.

Referring to the drawings:

Fig. 1 shows a telephone system comprising a toll office TO and a local ofi'ice L0; and

Figs. 2 and 3 show a signal receiving circuit SR and an associated sender circuit SDR).

The toll ofiice TO, which comprises a toll board and a number of operators positions thereat for answering calls incoming from local and other toll offices and for extending connections to other toll offices and to local offices, is represented in the drawings by an operators position equipment OP which includes a key-set for controlling the sending of selective signals, a cord CD, two jacks J l and J2 and an outgoing trunk circuit OT connected'to jack J2. The local office LO, which comprises switches for completing local and incoming calls and switches for connecting calling subscribers lines to outgoing trunks is represented in the drawings by the incoming trunk circuit IT, signal receiving circuit SR, sender circuit SDR, incoming selector IS, connector C, and a called subscribers station B. The signal receiving and sender circuits are common to a plurality of incoming trunk circuits. Upon seizure of a trunk T terminating in office LO, a link circuit connects the incoming trunk circuitv IT with an idle signal receiving circuit SR and with an idle sender circuit SDR.- Reference may be had to the patent to Carpenter et al. 1,780,906 of November 11, 1930 and the patent to Henry et al. 1,916,761 of July 4, 1933, for disclosure of systems including operators positions equipped with key-sets and including senders arranged to receive selective signals transmitted upon operation of the various keys of the key-set.

The key-set in the toll office will, in addition to the numerical keys, comprise a KP key, the operation of which transmits a signal to condition the signal receiver SR for response to numerical signals, the ten numerical keys, a start key for use when immediate ringing of the subscribers station is desired and a start key for use when ringing is to be started under the control of ringing key in the operators cord circuit.

. Each of these kays, with the exception of theIQ? key, will be arranged to effect the transmission of signaling current of a different oneof twelve different frequencies in the Voice range. The KP key will be arranged to effect the transmission of a signal consisting of current of a first particular one of the twelve frequencies followed by current of a second particular one of the twelve frequencies. For instance, the KP signal may consist of current of the frequency fl used for sending the digit 1 followed by current of the frequency f5 used for sending the digit 5. The twelve frequencies fl to jl2' are spaced apart to be adapted for selectiveioperation of the signal receiver SR; for instance, the

frequencies used may be 425, 485, 550, 630, 720, 820, 925, 1060, 1190, 1380, 1565. 1770.

The sender SDR, which is represented in the drawings by the register and control relays lEll to H2, inclusive, comprises means for sending impulses to control the operation of the incoming selector IS, intermediate selectors (if any), and a connector C.

The signal receiver SR, which is shown in detail in Figs. 2 and 3, consists of an input transformer 2, the primary winding of which is connected to and through incoming trunk circuit IT to the conductors of a trunk line T, a threeelement thermionic amplifier tube 3, a three-element voltage-limiting thermionic amplifier tube ID, a transformer 4 coupling the output of tube 3 to the input of tube l3, twelve filters Fl to Fl 2, inclusive, each tuned to a different one of the twelve signaling frequencies fl to fl2, inclusive, transmitted by operation of the various keys of an operators key-set in the toll office TO, twelve rectifiers Rl to Rl2, inclusive, twelve signal relays II to 22, inclusive, and auxiliary relays 34 to 31, inclusive. The filters F2, F3, F4 and F6 to Fl2, inclusive, are normally shortcircuited by the lower back contact of relay 3'! and for this reason relays l2, l3, l4 and Hi to 22, inclusive, are normally inoperative. The contacts of relays ll and I5 are normally held in the position shown in this drawing by the energization of their middle, biasing windings in series. The biasing winding of relay I5 is normally further energized in series with resistor 36 so that relay I5 is not operatively responsive to signaling current; and relay ll is, therefore, the only one of the twelve signal relays normally operable. Upon receipt of a conditioning signal, that is, a signal comprising current of frequency fl followed by current of frequency f5, relay H is operated by the current of frequency H to render relay l5 operable and relay I5 is then operated by current of frequency f5 to effect the operation of relay 31, as hereinafter described. Relay 31 opens the short circuit around filters F2, F3, F4 and F6 to FlZ, inclusive, and thus renders all of relays II to 22 operable.

Signaling currents and also voice currents are transmitted through transformer 2, amplifier tube 3 and transformer 4 to the grid of tube la. The resistor 8 in series with the grid of tube l3 limits the voltages impressed on the grid so that tube It] acts as a peak limiting amplifier to' pass at any one time only enough energy to the tuned circuits Fl to Fl2, inclusive, to effect the operation of one of the signal relays H to 22, inclusive. If all the energy thus passed is of one of the twelve signaling frequencies, the corresponding signal relay is operated; but if the energy thus passed includes more than one of the signaling frequencies or includes energy from voice currents or other interfering currents, the amount of energy of each frequency to which filters Fl to Fl2 are tuned is insufiicient to effect the operation of the associated signal relay.

Assume now that a KP signal is transmitted over trunk T to the signal receiver SR, the primary winding of transformer 2 being thereby energized by current of frequency fl followed by current of frequency f5. Since filter Fl is tuned to constitute a very high impedance at frequency fl, and while substantially all of the energy in the output circuit of tube I6 is of this frequency, the voltage impressed across the left winding of relay ll effects the operation of relay ll, none of the other signaling relays being operated. The operation of relay ll closes a circuit including resistor 29 for charging condenser 33. When the current of frequency fl ends, relay ll releases, closing a circuit for discharging condenser 33 through the winding of relay 34, the capacity of condenser 33 being sufficient to maintain the operative energization of relay 34 for about .030 second. Relay 34 opens the circuit through resistor 36, thereby decreasing the biasing current through the middle winding of relay IE to render this relay operable by its left winding in response to current of frequency f5. If current of frequency f5 is received while relay34 is operated, and substantially all of the current is of frequency f5, and since the filter F5 is tuned to constitute a very high impedance at frequency f5, the voltage impressed across rectifier R5 and the left winding of relay l5 effects the operation of relay l5, none of the other signaling relays being operated. Relay l5 closes a circuit for operating relay 35; relay 35 closes a circuit for operating relay 36; and relay 36 locks through its lower front contact and conductor IM to ground in the associated sender circuit SDR. When the current of frequency f5 ceases, relays l5 and 35 release in succession. The release of relay 35 closes a circuit including the upper front contact of relay 36 for operating relay 3?. Relay 31 disconnects resistor 29, condenser 33 and relays 34 and 35 from the contacts of relays ll and I5 and connects these contacts to control the energization of the windings of register relays l6l and I05 of the sender circuit SDR. Relay 31 also opens the short circuit around filters F2, F3, F4 and F6 to Fl2, inclusive, thereby rendering all of relays ll to 22 selectively operable responsive to signaling current transmitted over trunk T due to the operation of the numerical keys and start key at a calling operators position in office TO.

If, after the operation of relay 31 in response 'to a KP signal, current of frequency fl is received alone, relay ll operates, closing a circuit for operating register relay llil of sender SDR. The operation of relay ll also opens a short circuit across the right winding of relay ll, thereby causing the charging of condenser 30 through this winding in series with resistors 3| and 32. The right winding of relay ll is thus energized to hold relay ll operated for a minimum of 0.30 second, even though the current of frequency fl does not continue for this length of time, to insure the operation of the register relay llll in the sender circuit. If current of frequency f5 is received alone, relay l5 operates, closing a circuit for operating register relay I05 and opening a short circuit around the right winding of relay l5 to charge condenser 40 through this winding in series with resistors ll and 42 so as to maintain the energization of relay l5 long enough to insure the operation of register relay I65.

If current of any oneof frequencies f2, f3, f4 and f6 to fl2, inclusive, is received alone, the corresponding one of relays l2, l3, l4, and Hi to 22, inclusive, is operated, the operation of each being maintained for a long enough time to insure the operation of the corresponding register relay by the charging of a condenser through its right winding in a similar manner to that in which the operation of relays l l and I5 is maintained as above described.

When the sender has completed its control of the switches through which connection with the called subscribers line is completed, the sender and signaling circuits are released, the disconnection of the holding ground from conductor I60 causing the successive release of relays 36 and 31 to return the signal receiving circuit SR. to normal.

What is claimed is:

1. A signal receiver normally adapted to respond to a first signal consisting of current of a first particular frequency followed within a predetermined interval of time by current of a second particular frequency, and thereafter adapted to selectively respond to any one of a plurality of signals, each of said plurality of signals consisting of current of a different one of a like plurality of frequencies including said first and second particular frequencies, said receiver comprising signal relays, one for each of said frequencies, means for selectively passing to the operating winding of each of said relays signaling current of a different one of said frequencies, means normally rendering all of said signal relays except the two relays adapted for operation by current of said first and second particular frequencies operatively non-responsive to signaling current, and means rendered effective by the successive operation of said two relays in response to said first signal for rendering all of said relays selectively responsive to signaling current.

2. A signal receiver normally adapted to respond to a first signal consisting of current of a first particular frequency followed within a predetermined interval of time by current of a second particular frequency, and thereafter adapted to selectively respond to any one of a plurality of signals, each of said plurality of signals consisting of current of a different one of a like plurality of frequencies including said first and second particular frequencies, said receiver comprising signal relays, one for each of said frequencies, means for selectively passing to the operating winding of each of said relays signaling current of a different one of said frequencies, means comprising a control relay normally rendering all of said signal relays except the two relays adapted for operation by current of said first and second particular frequencies operatively non-responsive to signaling current, and means including said two relays responsive to said first signal for operating said control relay to render all of said relays selectively responsive to signaling current.

3. A signal receiver normally adapted to respond to a first signal consisting of current of a first particular frequency followed Within a predetermined interval of time by current of a second particular frequency, and thereafter adapted to selectively respond to any one of a plurality of signals each consisting of current of a different one of a like plurality of frequencies including said first and second particular frequencies, said receiver comprising signal relays, one for each of said frequencies, means for selectively passing to the operating winding of each of said relays signaling current of a different one of said frequencies, means comprising a control relay normally rendering all of said signal relays except the two relays adapted for operation by current of said first and second particular frequencies operatively non-responsive to signaling current, means comprising a biasing winding of the signal relay adapted for operation by said second particular frequency normally rendering said rela inoperable, means including the signal relay adapted for operation by current of said first particular frequency for decreasing the energization of said biasing winding to render the relay operatively responsive for a predetermined interval of time to signaling current of said second particular frequency, and means including said two relays for operating said control relay to render all of said signal relays operatively and selectively responsive to signaling current.

4. In combination, a line and a signal receiver connected to said line, said receiver comprising a plurality of signal relays, means selectively connecting an operating winding of each of said relays to said line, said means including filters, one for each relay, each filter tuned to pass to the associated relay current of a different one of a corresponding plurality of frequencies used for signaling over said line, control means rendering all of said relays except a first particular one of said relays non-responsive to signaling current, means rendered effective by the operation of said first relay for rendering a second particular one of said relays operable for a predetermined interval after said first relay releases, and means operated responsive to the operation of said second relay within said interval after said first relay releases for rendering all of said relays operable in response to succeeding signals.

5. In combination, a line and a signal receiver connected to said line, said receiver comprising a plurality of signal relays, means selectively connecting an operating winding of each of said relays to said line, said means including filters, one for each relay, each filter tuned to pass to the associated relay current of a different one of a corresponding plurality of frequencies used for signaling over said line, control means rendering all of said relays except a first particular one of said relays non-responsive to signaling current, means rendered effective by the operation of said first relay for rendering a second particular one of said relays operable for a predetermined interval after said first relay releases, and means operated responsive to the operation of said second relay within said interval after said first relay releases for rendering all of said relays operable in response to succeeding signals, each consisting of current of only one of said frequencies.

HENRY E. VAUGHAN. 

